The present invention relates to a tilting speed controlling apparatus in an industrial vehicle such as a forklift. More particularly, the present invention pertains to a control apparatus and method for controlling tilt cylinders, which tilt a mast that supports a load carrier. The load carrier can be lifted and lowered.
A typical industrial vehicle such as a forklift includes a mast pivotally supported on the front of the vehicle. The forklift also has a fork supported by the mast, which may be lifted and lowered. A tilt lever is provided in the cab. The operator manipulates the tilt lever to actuate tilt cylinders, which tilt the mast forward or rearward. Tilting of the mast facilitates loading and unloading and improves the stability of the vehicle while running.
When the mast is tilted forward, the rear wheels of the forklift must be prevented from losing contact with the road surface. That is, the stability of the vehicle must be guaranteed. Japanese Unexamined Patent Publication No. 7-61792 discloses an engine type forklift that maintains contact between the rear wheels and the ground. The forklift includes an electromagnetic valve that is located in an oil passage connected to a pair of tilt cylinders. The opening size of the electromagnetic valve is controlled in accordance with manipulation of the tilt lever, which controls the tilting speed of the mast.
When the weight of an object on the load carrier is greater than a predetermined value and the height of the load carrier exceeds a predetermined height, the apparatus limits the opening size of the control valve such that tilting speed of the mast is limited. That is, according to the weight of a carried object and the height of the load carrier, the tilting speed mode is switched between a normal tilting speed mode and a low tilting speed control mode. The apparatus thus prevents the rear wheels from losing contact with the road surface due to a high forward tilting speed of the mast.
A battery-powered forklift includes a pump, which is driven by an electric motor. The pump sends oil to a hydraulic circuit to actuate a lift cylinder and tilt cylinders. When a lift lever is manipulated, the motor is started and sends hydraulic oil to the lift cylinder and the tilt cylinders.
The tilting speed of the mast varies in accordance with the degree of movement of the tilt lever both in the normal tilting speed mode and the low tilting speed mode. However, the forklift of the publication has only two tilting speed modes. Thus, switching between the two modes may disturb the operator. Also, the tilting speed may be too slow, which lowers performance. Further, the tilting speed may be too fast, which prevents the mast from being finely controlled.
To avoid such disadvantages, one or both of the height of the load carrier and the weight of the carried object may be continuously monitored, and the tilting speed may be continuously changed in accordance with the change of the center of gravity of the mast. This requires that the opening size of the electromagnetic control valve be continuously changed in accordance with changes of the detected value, which complicates the control procedure.
Since the height of the load carrier and the weight of the carried object both need be detected, the forklift must include a height sensor and a load sensor. If the apparatus is installed in a battery-powered forklift, an extra electromagnetic control valve also needs to be installed, which complicates the control procedures and the structure of the forklift.
Accordingly, it is an objective of the present invention to provide a tilting speed controlling apparatus that optimizes the tilting speed of a mast.
To achieve the above objective, the present invention provides a tilt speed control apparatus for an industrial vehicle, the apparatus comprises a mast pivotally supported on a body frame. A load carrier is supported by the mast. The load carrier is lifted and lowered and is constructed to carry a load. A tilt cylinder tilts the mast. A pump sends hydraulic oil to the tilt cylinder. A motor drives the pump. An operating member is actuated to tilt the mast. An operating detector detects that the operating member has been actuated. A position detector produces a signal relating to the height of the load carrier. A controller controls the motor. When the operating detector detects that the operating member has been actuated, the controller controls the motor according to the signal such that the speed of the motor is relatively low when the position of the load carrier is relatively high.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.